The present invention relates to an apparatus and method for finishing contoured optical surfaces in accordance with particular prescriptions, and more directly, to such apparatus and methods incorporating work surfaces which are selectively conformable to a broad range of optical surface curvatures for performing work operations on these surfaces.
Optical surfaces of eyeglass lenses are typically prepared in accordance with particular lens prescriptions that require the lens have that contours which provide selected focusing or other optical effects. The contours may be convex or concave, and a lens may be provided with both convex and concave surfaces that act together to produce the desired optical effect. Generally, the surface of an eyeglass lens proximate to the eye, is ground with a concave contour made up of compound curves. A toric surface is found on many ophthalmic lenses, and has the contours of a section of a toroid or donut. In general, there are two basic curvatures on a toric surface, one corresponding to the radius of the equator and the other corresponding to the radius of the tubular element forming the toroid. These two curvatures are referred to respectively as the xe2x80x9cspherexe2x80x9d and the xe2x80x9ccylinderxe2x80x9d, and together with the xe2x80x9caxisxe2x80x9d angle of the cylinder, the spherical curvature of the front surface and the index of refraction of the lens material define the prescription power of the lens.
Conventional methods for finishing the prescription surface of an ophthalmic lens utilize a lap having a specially contoured surface that substantially matches the contours of the desired prescription surface of a lens being finished. A thin finishing pad is attached to the contoured surface of the lap, typically by adhesive, and an abrasive material is either directed onto the pad in the form of a slurry or is incorporated into the pad itself. Typically, pads with an abrasive material bonded or otherwise integrated into them are referred to as fining pads and are used for coarser finishing operations. Fibrous pads without abrasives are used with a slurry containing fine abrasive materials are referred too as polishing pads. Unless otherwise specifically stated, the term xe2x80x9cfinishing padxe2x80x9d is utilized throughout this specification to refer to both types of pads, and the term xe2x80x9cfinishingxe2x80x9d is used throughout this specification to refer to both types of operations.
Since the finishing pad in conventional finishing operations is relatively thin and must take its shape from the lap, the lap in turn must be ground with contours that essentially conform to the prescription or curvatures of the lens being finished. As a consequence, finishing laboratories must stock a large number of laps corresponding to the full range of prescriptions that are commonly required. Needless to say, a significant inventory of laps is needed.
Alternatively, an individual lap can be ground for each prescription as needed. U.S. Pat. No. 4,989,316 issued to Logan et al. and assigned to the Assignee of the present invention, describes a numerically-controlled machine for cutting a lens blank and a corresponding lap blank to be used in finishing the lens blank.
As a further alternative, the lens blank from which the eyeglass lens is formed can be coarsely ground to the desired prescription, and a conformable lap can be used as the tool for the finishing operation. A conformable lap in general has a work surface that is adapted to conform to the curvature of the contoured surface ground on the lens blank. Thus, during a finishing operation which may employ a fining or polishing pad with slurry, the coarseness of the contoured surface is removed but the general curvatures defined by the prescription are preserved. Conformable laps are shown in U.S. Pat. Nos. 4,831,789; 5,095,660; 5,345,725; and 5,593,340, French Patent No. 2654027 as well as European Application No. 0 655 297.
It is an object of the present invention to provide conformable laps which may conform to the contours of optical surfaces having a wide range of curvatures, and a related method for finishing such optical surfaces.
The present invention is directed to a conformable lap for finishing optical surfaces, such as ophthalmic lens surfaces, and to a related method for finishing such surfaces. The conformable lap comprises a rigid base surface defining a nominal curvature, such.as an ophthalmic lens curvature, corresponding to a predetermined range of curvatures. A work surface, preferably a-thin, hard, polymeric surface, extends adjacent to the base surface for contacting a selected optical surface and conforming to the curvature of the optical surface. A selectively conformable substance of the lap forms a layer extending between the rigid base surface and the work surface, and is selectively changeable between solid and non-solid forms. In its non-solid form, the selectively conformable substance permits movement of the work surface relative to the base surface to conform to the curvatures of any one of a plurality of optical surface curvatures within the predetermined range of curvatures, and in its solid form the substance fixes the work surface in a position conforming to the curvature of a selected optical surface and retains the conforming position during finishing of the selected optical surface.
In the preferred embodiment, the selectively conformable substance is a mixture of thermoplastic and other more thermally-conductive particles, such as aluminum, and is changeable from its solid to its non-solid form in response to the application of thermal energy thereto.
One feature of the present invention is that the temperature-controlled fluid is introduced through a discharge end of a fluid channel to change the conformable substance from solid to non-solid form and vice-versa. The discharge end includes at least one central opening to introduce relatively hot fluid to a substantially central portion of the base surface and a plurality of openings to introduce relatively cold fluid to side portions of the base surface. The discharge end of the present invention ensures that the conformable substance cools to accurately assume the shape of the lens.
One advantage of the present invention is that the conformable lap may rapidly and accurately conform to a selected optical surface curvature to accurately finish, for example, an ophthalmic lens surface. Another advantage of the present invention is that a limited number of conformable laps may be provided, wherein each lap may conform to any of a plurality of different ophthalmic lens curvatures within a predetermined range of curvatures.
Other advantages of the present invention will become apparent in view of the following detailed description and accompanying drawings.